The anti-inflammatory effect of exercise

The main job of the immune system is to protect the body against infection and harmful stimuli. It does this by mounting an inflammatory response that involves activation of immune cells, increased blood flow to the damaged or infected tissue, and the release of specific molecular signals such as cytokines, all of which contribute to tissue repair.

Inflammation is therefore a vital homeostatic response. However many chronic diseases, including metabolic and cardiovascular diseases, have a significant inflammatory component. The discovery that exercise has anti-inflammatory effects has thus revealed an important additional health benefit of regular exercise.

Sedentary behaviour and inflammation

Sedentary behaviour increases the risk of development of obesity, type 2 diabetes, cardiovascular disease and various cancers, all of which are linked with inflammation. Accumulation of adipose tissue, or body fat, associated with physical inactivity may be a biological trigger for development of this inflammatory state.

Adipose tissue is not merely a fat store; excess visceral adipose tissue deposits can be infiltrated by immune cells that release pro-inflammatory cytokines, leading to chronic low-grade inflammation in the body that is associated with development of non-communicable disease.

How is exercise anti-inflammatory?

Exercise causes the release of the hormones adrenaline and cortisol from the adrenal glands, and the cytokine IL-6 from working muscles. These molecular mediators suppress inflammation, thus inducing an anti-inflammatory environment within the body.

Repeated bouts of exercise repeatedly induce this anti-inflammatory environment, in the long term lowering the risk of development of diseases that are triggered or exacerbated by inflammation.

Is there a downside?

Perhaps, if you are an elite athlete! Remember that inflammation is a vital response that protects us against infection. So, the downside of suppressing inflammation is the potential risk of mounting an insufficient immune response to viruses or bacteria.

It it is well-known that moderate exercise is associated with a decreased incidence of respiratory tract infection compared with sedentary individuals or elite athletes – see the ‘J-shaped curve’ below (Nieman et al, 1990).

However, the many benefits of regular high-intensity exercise to health reaped by elite athletes outweigh the potential downside of the increased susceptibility to minor infections.

The key take-home message is that exercise has anti-inflammatory effects which can lower the risk of development of diseases that are triggered or exacerbated by inflammation.